Method of chlorinating hydrocarbons



Dec. 15, '1936.

.L H. CLARK METHOD OF CHLORINATING HYDROCARBONS Filed Feb, 1, 1934 Patented Dec. 1.5, 1936 UNITED STATES METHOD 0F CHLOBINATING HYDRO- CARBONS Lee H. Clark, Groe lle, Mich., assigner to The Sharples Solvents Corporation,

Pa., a corporation of Philadelphia, Delaware Application February l, 1934, Serial No. '109,394`

2 Claims.

'I'he present invention relates to the vapor phase chlorination of hydrocarbons and hydrocarbon substitution products and it has had as its principal object the development of a method of chlorinating these compounds in such a manner as to eiiect an adequate control of the end products' to selectively produce desired mono or poly-chlorination products.

Further objects of the invention pertain to the avoidance of the formation of undesired products such as unsaturated hydrocarbons, carbon, gummy residues and undesired polychlorides in the perfomance of chlorination reactions and to the development of a process of chlorination which eiectively affords novel and adequate provision for the avoidance of the danger of explosion and facilitates the economical large scale separation of the reactants from the resultants of the reaction.

The problems oi' explosion and degradation of the end products resulting in the production of undesired products have been among the principal diiiiculties heretofore encountered in the practice of chlorination of hydrocarbons. Where ignition is allowed to persist, decomposition of the chlorinated hydrocarbon into unsaturated compounds and/or carbon and hydrogen chloride frequently occurs and explosions are sometimes caused by the heat generated in the decomposition reactions. In the case of hydrocarbons having more than two carbon atoms, decomposition 'is additionally objectionable because of the nature of thev products obtained when the unsaturated hydrocarbons formed by such decomposition recombine with h'ydrogen chloride which is present. Thus where primary amyl chloride is decomposed into pentene 1, this pentene l tends to recombine with the hydrogen chloride split oli from the amyl 'chloride molecule. Such recombination almost invariably results in the formation of a secondary amyl chloride. as indicated by the yfollowing equations:

In the case of the initial chlorination loi? iso pentanes to form iso-amyl chlorides', the corresponding decomposition and addition reactions result in the formation of tertiary amyl chloride. As these secondary and tertiary chlorides are' less desired than the primary chlorides, it is evident that it is usually desirable to avoid reactions such as those indicated` above, and it has been a purpose of the present invention to minimize them. f

The problems discussed above are particularly n) acute in connection with attempts to re-chlorinate chlorinated hydrocarbons to produce polychlorinated derivatives of the hydrocarbons. The present invention, therefore, has as an additional object the vapor phase production of poly- 15 chlorhydrocarbon derivatives in such a manner as to carefully control the nature of the chlorinated derivatives produced and avoid excessive decomposition resulting in the production of unsaturated compounds and other undesired prod- 2o ucts.

In the practice of. the invention, the chlorine and the hydrocarbon are fed to the zone of reaction 'in the presence of an inert gas which serves as a diluent for the reacting constituents and thus absorbs a large part of the heat of reaction and prevents occurrence of ignition and explosions. In the preferred embodiment, the gas which serves as a diluent is the hydrogen chloride formed as a byproduct in the practice of ,o the invention. By making use of the hydrogen chloride formed, it is possible to eect the desired dilution without entailing the expense incident to the purchase oi a special gas for use in this connection. The use of `this gas also precludes the necessity. of a special step in the process or special apparatus for separating the diluent vfrom other constituents of the mixture after the completion of the chlorination reaction. As hydrogen chloride formed in the reaction must be separated from the remainingconstituents in any case, the portion of the hydrogen chloride which is to be separated may be separated wlthout adding serious complications to the method or apparatus. 5 The use of hydrogen chloride as a diluent has important advantages from a chemical standpoint in addition to these advantages from the standpoint of plant operation. Thus, the chemical eilect of the presence of a large quantity of `hydrogen chloride in the mixture tf ids tominimize the decomposition of the hydrocarbon chlorides. As the hydrogen chloride is a resultant of such decomposition reaction as indicated by Equation 1, above, its presence in excess operates in accordance with the laws of mass action to preclude the decomposition of the chlorinated hydrocarbons into unsaturated compounds and the incidental subsequent combination of these unsaturated hydrocarbons with hydrogen chloride to form undesired secondary and tertiary chlorides.

The details of procedure involved in the practice of the present invention will be better understood by reference to the attached flow sheet. In the practice of the process as illustrated, hydrocarbon which is to b chlorinated is drawn from a storage tank I0 to a pump II and fed by this pump to a tank I2. From the tank I2 it is fed by a pump I3 through valve I4 to a vaporizer I5. The hydrocarbon vapor is then passed `through a valve I6 to a mixing zone I1 where it is mixed with chlorine from tank Ill', the chlorine being vaporized at I5 during its flow from the storage tank I0' to the mixing zone I1.

' The mixed gases may be passed from the zone I1 through a reactor I8 in which the chlorination reaction takes place. While the reactor I8 may be of any known type and may depend upon the eifect of light, heat or catalyst to effect'the chlorination of the hydrocarbon without departing from the 4spirit of the invention, the preferred embodiment of the invention involves the chlorination of the hydrocarbon under the influence of heat, as taught in the patent to Ayres No. 1,717,136 of June ll, 1929. The rate of flow at the zone of confluence between the hydrocarbon and chlorine vapors should also be rapid, las taught in that patent, in order that explosions and persistence of ignition may be avoided. During the initial stages of the chlorination procedure, the quantity of hydrocarbon fed tothe reaction zone should be in large excess of the molecular ratio involved in the reaction. By the observance of these precautions, it is possible to minimize the formation of poly-chlorides by the same expedients by which explosions and ignition are avoided.

As an alternative to the operation discussed in the preceding paragraph, the hydrocarbon and chlorine may be heated in the vaporizers I5 and I5 to temperatures suiiiciently high to cause prompt reaction between them when they are passed into confluence with each other, as indicated at I1. In case such high temperatures are attained in connection with the heating operations, it will be unnecessary to provide a reactor I8 as a separate element from the mixing zone I1 and this mixing zone will, therefore, become in eiect the reactor.

By the above-described chlorination reaction, a mixture of chlorinated hydrocarbon;A unconverted hydrocarbon and hydrogen chloride is formed. This mixture is passed through a cooler I9 to a f ractionating column 20, where the chlorinated hydrocarbon is condensed and separated from the hydrogen chloride and unchlorinated hydrocarbon passing from the reaction zone. A reflux of hydrocarbon is established into the top of column 20 in order to effect the desired fracltionation, the valve 3| being opened to admit hydrocarbon from the tank I2 for this purpose. The mixed vapors of hydrogen chloride and hydrocarbon pass from the top of column 20 through lines 22 and 23 into a condenser 24. In this condenser, the hydrocarbon condenses from a non-condensing mixture of hydrogen chloride and hydrocarbon vapors. Separation of the liquid from the gas occurs in the tank I2 after the mixture has passed from the condenser 24 into that tank.

After operation has been conducted for some time in the manner described above, a pressure due to the presence of the non-condensed hy-v drogen chloride and hydrocarbon vapors will be developed in the system. The valve 25 is then opened and a mixture of air, which originally filled the system, hydrogen chloride and hydro carbon vapor is allowed to pass through the valve 25. The rate of emission of gas through this valve is carefully controlled to maintain a steady desired pressure within the system. The mixed gases withdrawn through the valve 25 may be passed-through any conventional equipment for the absorption of hydrogen chloride in water to form hydrochloric acid of commercial strength. The tail gas from this operation is compressed and cooled to recover hydrocarbon, which may then be returned to the storage tank for re-introduction into the system, as required. The absorption, compression, condensing and collection equipment are not shown. The valve 51 may be wholly or partially opened during the chlorinating operation if desired, thus enabling the operator to recycle* material passing through this valve without passing such material through the condenser 24.

When the system has been purged of air by the emission of gases through the valve 25, valve 26 is opened so that the mixed vapors of hydrogen chloride and hydrocarbon from the tank I2 will pass through valve 26 and compressor 21 and valve. 30 to the mixing zone I1, whence they are recycled through the reactor and fractionation apparatus. In this connection, it is important to note that recycled gases are mixed with fresh hydrocarbon in the zone 51 before this hydrocarbon is contacted with chlorine at I1. The possibility of ignition is thus minimized by the preliminary dilution of the hydrocarbon.

The valve 29 may be opened during a part of the chlorinating operation if desired, thus allowing a part of the mixture of hydrocarbon and hydrogen chloride to be passed to the storage tank 28. The mixture of gases stored in this tank may be fed to the chlorinating apparatus during the preliminary stages of subsequent chlorination operations prior to the formation of these gases in the operation of the system insufficient quantity to develop the necessary pressure for continuous recycling in suiiicient quantities to eilect the desired dilution.-

When the lower boiling hydrocarbons are being chlorinated, it will be possible to vaporize so much hydrocarbon in the vapor from the tank I2 that the introduction of hydrocarbon through the pump I3 tothe vaporizer I5 may be discontinued. In this case, valves I4 and I6 will be closed and valves 25 and 30 manipulated to maintain a sufficient volume of returned vapors to eiect the desired mixture with the chlorine fed to the zone of coniiuence.

When higher boiling hydrocarbons are introduced, it will be undesirable to maintain temperatures in the tank I2 suflicient to vaporize hydrocarbon freely into the hydrogen chloride gas. vThe entire supply of hydrocarbon must then be fed to the zone I1 through the vaporizer I5. In this connection it should be noted that the temperature attained in the vaporizer must be sunicient to overcome the cooling effect of gases meeting at the zone of conuence 51 of the fresh hydrocarbon and other gases.

From the above discussion, it will be seen that the relative amounts of hydrocarbon introduced into the system through the vaporizer I and through vaporization into the vapor stream passing upwardly through the tank I2, depends upon the hydrocarbon under treatment. cautions, however, must be taken in connection with either method of introduction to insure a suiiicient dilution of the reactants by the hydrogen chloride and/or excess hydrocarbon present to avoid ignition or explosion.

When it is desired to produce poly-chlor derivatives of the hydrocarbon material under .treatment, the chlorinated products condensed inthe fractionating column 20 may be continuously passed through the valve 2| to a column 32. Heat is applied to material entering this column by means of a heater 33, which may be heated by steam or direct re and indirectly heats the material in the column 32 by continuous passage of heated liquid between the heater and the column through conduit 55. Conditions in the column 32 may be maintained at a temperature and pressure adapted to condense the poly-chlorides to the exclusion of the mono-chlorides passing through the column. Mono-chloride material passing from the column 32 is condensed at 35 and refluxed to the column through the valve 36. When the proper conditions of reflux have been established, a certain proportion of the chlorinated material may be withdrawn to container 40 at the desired rate by opening the valves 31 and 39 and restricting the rate of ow through the valve 36, if necessary.

Any desired portion of the chlorinated hydrocarbon passing tothe tank 40 may be passed through the line 42 by the pump 4| tovaporizer I5 and recycled through the system in contact with fresh chlorine to eiect the rechlorination of such chlorinated hydrocarbon to form poly-chlorides, and other chlorinated hydrocarbon material reaching the tank 40 may be withdrawn for use without being subjected to rechlorination.

It may be desired, in some cases, to effect the rechlorination of only a particular mono-chloride isomer or group of isomers. In such case, the mono-chlorinated material may be fractionated by closing the valve 39 and opening the valve 38 to allow passage of the chlorinated hydrocarbon into column 43 where it is heatedby means of a heater 44 Which is analogous to the heater 33 which causes vaporization of the monochlorides in the column 32. The overhead fraction from the colunm 43 is condensed vat 45 and reuxed through valve 46 to the top of the column until proper reilux conditions are established. 'I'he valve 41 is then opened to allow a certain proportion of the overhead product to be passed to the tank 49 or separately collected, as may be desired. Liquid material collecting at the bottom' of column 43 is withdrawn through valve 48 and returned to the tank 40 or .withdrawn from the f system as may be desired.

In the operation of this portion of the system, when a portion of the overhead fraction of the column 43 is to be rechlorinated, the valves 54 and 49 will be closed and valves 52 and 5I opened in order that the overhead product may be passed to the tank 40 from which it may be recycled after its separation from the liquid derivative in the column 43. In this case, the higher boiling material is separately collected by passage through the valves 48 and 5| and line `50 to a suitable receptacle. If, on the other hand, it is desired to re-chlorinate a portion of the higher boiling material passing through the column 43, valves Careful pre- I5I and 52 are closed and valves 49 and 54 are opened toallow the higher boiling liquid passing from the column 43 to lbe passed to the tank 40 and the overhead product to be separately collected by passage through the valve 54 to a suitable receptacle connected with the line 56. It will thus be seen that by the application of the process described, desired chlorinated derivatives may be simultaneously formed and separately collected. By the passage of chlorinated derivatives from the tank 40 to the reaction zone, these chlorinated derivatives may be rechlorinated simultaneously with the chlorination of fresh hydrocarbon material.

The process described is adapted to the separate collection of a desired chlorinated fraction or to the collection of a portion of 'lany desired chlorinated fraction and the rechlorination of y another portion of that same fraction. Thus, the final product from the process may be dichloride alone, poly-chlorides of a higherorder than di-chlorides, poly-chlorides mixed with other poly-chlorides or mono-chlorides, or separate isomers of any of thesecompounds.

From the above description, it will be seen that the objects of the invention have been amply attained. By the simple feature of recycling hydrogen chloride formed in the reaction, a dilution of the hydrocarbon passing to the reaction is obtained, and the mixture so formed may be further diluted by the use of excess hydrocarbon as desired. By proper fractionation and recycling desired fractions of varying composition may be produced.

It will be evident from the above description that, by the practice of the above invention, a

dilution of the materials passing to the reactor is separately obtaining desired mono-chlor and,

poly-chlor derivatives or desired mixtures of monoand poly-chlor derivatives.

Modifications will be obvious to those skilled in the art. It may, for example, be found desirable in certain instances to collect chlorinated hydrocarbon formed in the practice of the process and to chlorinate this material separately from unchlorinated hydrocarbon by .using this chlorinated hydrocarbon as a source of supply in the same manner as the original hydrocarbon material from the supply tank l0. In view of the feasibility of adopting this and other alternatives, I do not wish to be limited except by the scope of the subjoined claims.

What I claim is:

1.1The process of chlorinating saturated aliphatic hydrocarbons containing three or more carbon atoms in vapor phase which comprises passing such hydrocarbons through a reactor in theA presence of chlorine, separating chlorinated derivatives formed in the reactor from Vundesired material by passing material from the reactor through a fractionating column while maintaining a reflux of hydrocarbons to be chlorinated in said fractionating column and thereby absorbing a portion of the reflux hydrocarbons in the aov of liquid hydrocarbons which it is desired to chlorinate and thereby saturating said hydrogen chloride with said hydrocarbons, passing said saturated hydrogen chloride to the reactor and concurrently passing liquid hydrocarbons from said body of liquid hydrocarbons through a vaporizing chamber into contact with said recycled saturated hydrogen chloride and through said reactor to thereby eiect chlorination of additional hydrocarbons.

LEE H. CLARK. 

